Technical Abstract: This study investigated the use of acid hydrolyzed algae to enhance the enzymatic hydrolysis of cellulosic biomass. We first characterized wastewater-grown algal samples and determined the optimal conditions (acid concentration, reaction temperature, and reaction time) for algal hydrolysis using dilute sulfuric acid. The optimal condition for algal hydrolysis (considering release of both protein and sugar) was 4% sulfuric acid (w/w) at 116 °C for 30 min. Under this condition, 66% of the total protein and 99% of the total carbohydrate were released into the algal hydrolysate. Neutralized algal hydrolysate was then tested as a reaction medium (replacing the pH buffer solution) for the enzymatic hydrolysis of alkaline treated anaerobically-digested fiber. Our results showed that net glucose yields from enzymatic hydrolyses containing undiluted algal hydrolysate were at least 65% higher than net glucose yields from control media (bovine serum albumin solution, citrate buffer or distilled water), It is likely that the increase in net glucose yield is due, in part, to the binding of hydrolyzed algal proteins to lignin. This binding protects cellulase from binding to lignin. This study demonstrates a potential approach of using wastewater-grown algae as a co-substrate to significantly enhance the enzymatic hydrolysis of lignocellulose materials.